Fluid streams comprising small constituents are produced by many chemical and combustion processes, such as, but not limited to, particulates in the exhaust gas stream of coal fired power plants. Such constituents may include, for example, vaporous forms of these constituents. For environmental and other reasons, it may be desirous to remove these constituents. Sorbents—the term “sorbent”, including, but not limited, to both “adsorbent” and “absorbent”—may be injected into the gas exhaust streams exiting power plant boilers to promote removal of these constituents. The dilute vapor can be removed by means of interaction of the vapor with the surface of the sorbent; however, the removal efficiency of sorbent injection can be limited, depending on a number of factors including the time the sorbent has to interact with the constituent and the entrainment of the constituents in the gas exhaust stream. A need exists for an improved system and method to promote improved removal of constituents from a fluid stream.
Additionally, in the use of the sorbent injection technology, collection devices, such as a fabric filter bag house, are frequently provided downstream of the sorbent injector. While sorbent injection is proven as one method of satisfying constituent emissions regulations—e.g., mercury emission regulations in facilities, such as coal-fired power plants, the use of such sorbents will typically increase the frequency of bag cleaning. For example, in the use of a sorbent, such as activated carbon, to remove a constituent, such as mercury, the cleaning frequency can be tripled as a result of activated carbon being injected at levels required to remove about 80% total mercury. Therefore, the increase in bag cleaning frequency becomes one of the greatest concerns with the use of sorbent injection to reduce constituent emission. It is clearly necessary to develop cost-effective methods to substantially reduce or eliminate the negative effects of sorbent injection on the fabric filter cleaning frequency.
In yet other situations, sorbents may be injected into exhaust streams and collected by other means such as electrostatic precipitators, cyclone collectors, gravitational settling chambers, and others. In these cases, bag cleaning is not an issue, but the cost of sorbents can be very high for a variety of reasons. In this case it is clearly necessary to develop methods to achieve more effective mercury removal for a given amount of injected sorbent, thereby reducing costs and/or improving mercury removal.
It is to such an acoustical stimulation system and method of vapor diffusion towards a surface that the present invention is directed.